Hi @DavieJoe,
@AntrikshSharma already answered your question but just a small reminder that the Extended Date table is an ISO-8601 type calendar so weeks always start on a monday.
You can try out the Basic date table here, which does allow you to set a StartOfWeekDay parameter of type number, where 0=Sunday … 6=Saterday
The parameter that @BrianJ highlighted only allows you to switch the weekday numbering from 0…6 (default) to 1…7